Computing devices such as personal computers, laptop computers, tablet computers, cellular phones, and countless types of Internet-capable devices are increasingly prevalent in numerous aspects of modern life. Over time, the manner in which these devices are providing information to users is becoming more intelligent, more efficient, more intuitive, and/or less obtrusive.
The trend toward miniaturization of computing hardware, peripherals, as well as of sensors, detectors, and image and audio processors, among other technologies, has helped open up a field sometimes referred to as “wearable computing.” In the area of image and visual processing and production, in particular, it has become possible to consider wearable displays that place a “near-eye display” element close enough to a wearer's eye(s) such that a displayed image is perceived by the wearer.
Wearable computing systems can be configured to be worn proximate a wearer's head to allow for interfacing with the wearer's audible and/or visual senses. For example, a wearable computing system can be implemented as a helmet or a pair of glasses. To transmit audio signals to a wearer, a wearable computing system can function as a hands-free headset or as headphones, employing speakers to produce sound. Audio transducers are employed in microphones and speakers. A typical audio transducer converts electrical signals to acoustic waves by sending the electrical signals through a coil to produce a time-varying magnetic field which operates to move a small magnet connected to a membrane. The time-changing magnetic fields vibrate the magnet, which vibrates the membrane, and results in sound waves traveling through air. An acoustic transducer can also translate sound waves to electrical signals by a similar process using a pressure sensitive membrane to create a time-changing magnetic field that produces an electrical signal in a coil of wire, such as in a microphone.
Sound perception in the biological realm, such as in human ears, also involves converting acoustic waves to electrical signals. For conventional sound perception, incoming acoustic waves are directed by the outer ear toward the ear canal where the tympanic membrane (ear drum) is stimulated to vibrate in accordance with the received acoustic pressure wave. The pressure wave information is then translated and frequency shifted by three small ossicles bones in the middle ear. The ossicles bones mechanically stimulate another membrane separating the fluid-filled chamber of the inner ear, which includes the cochlea. Hairs lining the interior of the cochlea act as frequency-specific mechanotransducers when stimulated by the pressure wave transmitted through the fluid in the cochlea to activate neurons that send signals to the brain allowing for perception of sound.
Bone conduction transducers create sound perception by directly stimulating the ossicles bones in the middle ear and effectively bypassing the outer ear. Bone conduction transducers couple to a bony surface on the skull or jaw, such as the mastoid bone surface behind the ear, to create vibrations that propagate to the ossicles bones, and thereby allow for sound perception without directly vibrating the tympanic membrane. A bone conduction transducer transmits vibrations to the inner ear by a vibrating anvil placed on a bony structure of the skull or jaw. Such a bone conduction transducer can include an anvil suitable for making contact with a bony portion of the head can be mounted to a transducer, which can vibrate the anvil according to received electrical signals.